1. Field of the invention
The present invention relates to a radiographic image detection device used for radiographic imaging.
2. Description Related to the Prior Art
Recently, radiographic image detection devices have been used for diagnostic imaging in medical fields. The radiographic image detection device converts radiation (for example, X-rays) applied from a radiation source and passed through an object of interest of a subject (patient) into charges and produces a radiographic image. There are direct-conversion type and indirect-conversion type radiographic image detection devices. The direct-conversion type radiographic image detection device directly converts the radiation into the charges. The indirect-conversion type radiographic image detection device converts the radiation into visible light, and then converts the visible light into the charges.
The indirect-conversion type radiographic image detection device comprises a scintillator (phosphor layer) and a photoelectric conversion panel. The scintillator absorbs the radiation and converts the absorbed radiation into the visible light. The photoelectric conversion panel detects the visible light and converts the detected visible light into the charges. The scintillator is made from cesium iodide (CsI) or gadolinium oxide sulfur (GOS). The photoelectric conversion panel is composed of an insulating substrate made from glass, and thin-film transistors and photodiodes arranged in a matrix over the surface of the insulating substrate.
Manufacturing cost using the CsI is more expensive than that using the GOS. However the CsI is superior in efficiency of converting the radiation into the visible light. The CsI has a columnar crystal structure and due to its light-guide effect, the CsI is superior in SN ratio of image data. For these reasons, the CsI is particularly used for the scintillators of high-end radiographic image detection devices.
“Laminated type” and “direct vapor deposition type” radiographic image detection devices, which utilize the CsI as the scintillator, are known. In the laminated type radiographic image detection device, a vapor deposition base, on which the scintillator is vapor-deposited, and the photoelectric conversion panel are laminated or adhered to each other through an adhesive layer such that the scintillator faces the photoelectric conversion panel. In the laminated type radiographic image detection device, distal end portions (hereinafter simply referred to as the end portions) of the columnar crystals of the CsI are in close proximity to the photoelectric conversion panel. The visible light released from the end portions enters the photoelectric conversion panel efficiently, so that a radiographic image with high resolution is produced. However, the use of the vapor deposition base in the laminated type radiographic image detection device increases manufacturing processes, resulting in high manufacturing cost.
In the direct vapor deposition type, the scintillator is directly vapor-deposited on the photoelectric conversion panel. The vapor deposition base is unnecessary in the direct vapor deposition type, so that the direct vapor deposition type has few manufacturing processes and low manufacturing cost. Since the end portions of the columnar crystals of the CsI of the direct vapor deposition type are disposed on the opposite side of the photoelectric conversion panel, the image quality of the radiographic image is inferior to that of the laminated type, but superior to that of the case where the scintillator is made from the GOS. Thus the direct vapor deposition type offers an excellent balance between performance and cost.
However, the direct vapor deposition type has a drawback that a part of the columnar crystals may grow abnormally or irregularly during the vapor deposition of the scintillator on the photoelectric conversion panel. Distal end portions (or simply referred to as the end portions) of the abnormally-grown columnar crystals (hereinafter referred to as the abnormally-grown crystals) may significantly protrude from the surface of the scintillator (see Japanese Patent Laid-Open Publication No. 2006-052980). The abnormally-grown crystals are columnar crystals grown on a local defect or the like having a convex shape or the like occurred on the photoelectric conversion panel. The size of the end portions of the abnormally-grown crystals expands to be greater than the size of the defect, on which the abnormally-grown crystals grow, as the end portions become away from the photoelectric conversion panel.
In the radiographic image detection device described in the Japanese Patent Laid-Open Publication No. 2006-052980, the scintillator is disposed on the radiation source side. In other words, the scintillator is disposed closer to the radiation source than is the photoelectric conversion panel. The radiation enters the scintillator from the end portions of the columnar crystals. The scintillator absorbs the radiation at around the end portions and generates the visible light. The configuration in which the scintillator is disposed closer to the radiation source than is the photoelectric conversion panel is referred to as PSS (Penetration Side Sampling) type.
In the PSS type, the radiation is incident on the end portions of the columnar crystals. In the case where the abnormally-grown crystals are present, the end portions of the abnormally-grown crystals also generate the light. Since the end portions of the abnormally-grown crystals expand significantly, the end portions generate a high amount of light, which causes an image defect in a radiographic image. To prevent or reduce the image defect, the end portions of the abnormally-grown crystals are crushed by application of pressure or the like after the scintillator is vapor-deposited on the photoelectric conversion panel.
ISS (Irradiation Side Sampling) type radiographic image detection devices of the direct vapor deposition type are known. In the ISS type, which has the configuration contrary to that of the PSS type, the photoelectric conversion panel is disposed closer to the radiation source than is the scintillator (see, for example, U.S. Patent Application Publication No. US 2012/0126124 A1 (corresponding to Japanese Patent Laid-Open Publication No. 2012-105879) and Japanese Patent Laid-Open Publication No. 2001-330677). In the ISS type, the radiation from the radiation source passes through the photoelectric conversion panel and then enters the scintillator. The scintillator generates the light in its portions on the radiation incidence side, close to the photoelectric conversion panel. Thereby, the light-receiving efficiency of the photoelectric conversion panel is improved. Thus, the ISS type produces radiographic images excellent in image quality and brightness.
In the ISS-type radiographic image detection device of the direct vapor deposition type, the radiation is incident on the photoelectric conversion panel side of the scintillator. Even if the abnormally-grown crystals are present, the radiation is incident on the proximal end portions of the abnormally-grown crystals and hardly reaches the distal end portions of the abnormally-grown crystals. For this reason, the amount of light generated in the distal end portions is small. In the ISS-type, the abnormally-grown crystals have little influence on the image, so that it is unnecessary to crush the end portions of the abnormally-grown crystals.
In a case where the photoelectric conversion panel with the scintillator is accommodated in a housing without crushing the end portions of the abnormally-grown crystals, the end portions, which protrude from the surface of the scintillator, may come into contact with the housing or the like and break when a load is imposed on the housing. The breakage of the end portions of the abnormally-grown crystals may cause damage to the adjacent normal columnar crystals. Since a circuit board, on which a signal processor for generating image data and the like are mounted, faces the scintillator in the ISS type, the end portions of the abnormally-grown crystals are likely to come into contact with and be crushed by the circuit board.